EP0467467A2 - Procédé de spectroscopie par résonance magnétique nucléaire - Google Patents

Procédé de spectroscopie par résonance magnétique nucléaire Download PDF

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Publication number
EP0467467A2
EP0467467A2 EP91201832A EP91201832A EP0467467A2 EP 0467467 A2 EP0467467 A2 EP 0467467A2 EP 91201832 A EP91201832 A EP 91201832A EP 91201832 A EP91201832 A EP 91201832A EP 0467467 A2 EP0467467 A2 EP 0467467A2
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EP
European Patent Office
Prior art keywords
frequency
pulse
frequency pulse
selective
gradient field
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP91201832A
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German (de)
English (en)
Other versions
EP0467467A3 (en
Inventor
Graeme Dr. Mckinnon
Peter Dr. Priv.-Doz. Bösiger
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Philips Intellectual Property and Standards GmbH
Koninklijke Philips NV
Original Assignee
Philips Patentverwaltung GmbH
Philips Gloeilampenfabrieken NV
Koninklijke Philips Electronics NV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Philips Patentverwaltung GmbH, Philips Gloeilampenfabrieken NV, Koninklijke Philips Electronics NV filed Critical Philips Patentverwaltung GmbH
Publication of EP0467467A2 publication Critical patent/EP0467467A2/fr
Publication of EP0467467A3 publication Critical patent/EP0467467A3/de
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/483—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy
    • G01R33/4833—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy using spatially selective excitation of the volume of interest, e.g. selecting non-orthogonal or inclined slices

Definitions

  • the invention relates to a nuclear magnetic resonance spectroscopy method, in which a sequence - preferably several times - acts on an examination area, which comprises two frequency-selective, the water component does not excite high-frequency pulses, between which there is a 180 ° high-frequency pulse and an arrangement for performing such a method.
  • the 180 ° high-frequency pulse is a so-called hard pulse, the frequency spectrum of which includes the Larmor frequency of water. Ideally - if this impulse tilts the nuclear magnetization everywhere by exactly 180 ° - the nuclear magnetization of water-bound protons in the examination area is not stimulated. In practice and in particular in examinations on the living body, however, there are slight deviations from this angle, which make the detection of the lactate or lipid components more difficult, if not impossible, because of the relatively high water concentration in the human body.
  • the second frequency-selective high-frequency pulse is followed by a further frequency-selective high-frequency pulse which does not excite the water component and that between the second frequency-selective high-frequency pulse and the further high-frequency pulse, as after the further high-frequency pulse, a magnetic gradient field is switched on and off in such a way that the temporal integrals over this gradient field before and after the further high-frequency pulse are equal to one another.
  • the further high-frequency pulse in connection with the magnetic gradient field before and after this pulse affects the nuclear magnetization of the protons bound to water on the one hand and the protons bound to lactic acid or fat on the other hand in different ways.
  • the protons bound to water do not "see” this pulse, and therefore their nuclear magnetization - if excited by the 180 ° pulse - is dephased, so that they cannot make a contribution to the nuclear magnetic resonance signal from the area under investigation.
  • the further high-frequency pulse has frequency components with the Larmor frequency of the protons bound to lactic acid or fat, it acts together with the preceding and the subsequent magnetic gradient field as a refocusing pulse, i.e. the dephasing which the nuclear magnetization of these protons experiences before the further impulse is canceled by the rephasing which they experience after this impulse.
  • the further high-frequency pulse in connection with the magnetic gradient field thus causes "water suppression".
  • the further high-frequency pulse is a 180 ° pulse.
  • the pulse can also have a flip angle other than 180 °, the greatest amplitude of the nuclear magnetic resonance signal (originating from lactic acid or fat) results at 180 °.
  • a further development of the invention provides that the further frequency-selective high-frequency pulse is followed by three 180 ° high-frequency pulses in the presence of a magnetic gradient field in each case and that the gradients of the magnetic gradient fields effective during these 180 ° high-frequency pulses are perpendicular to one another. This makes it possible to select a specific volume and to determine the lipid or lactate content only for this volume (localized spectroscopy).
  • An arrangement for carrying out the method according to the invention which is provided with means for generating a homogeneous stationary magnetic field, with a high-frequency coil arrangement for generating high-frequency pulses and for recording the nuclear magnetic resonance signals generated in response in the examination area, a processing unit for deriving a spectrum from the recorded nuclear magnetic resonance signals and with a control unit is characterized in that the control unit is designed such that it generates at least one sequence in which a first frequency selector A 90 ° high-frequency pulse for water suppression is followed by a 180 ° pulse, which in turn is followed by a second frequency-selective 90 ° high-frequency pulse for water suppression, after which a magnetic gradient field is switched on and off, followed by a further frequency-selective high-frequency pulse, after which the magnetic gradient field is switched on again - and is switched off.
  • the nuclear spin examination apparatus shown schematically in FIG. 1 contains an arrangement consisting of four coils 1 for generating a homogeneous stationary magnetic field, which can be in the order of a few tenths to a few T. This field runs in the z direction of a Cartesian coordinate system.
  • the coils arranged concentrically to the z-axis can be arranged on a spherical surface 2.
  • the patient 20 to be examined is located inside these coils.
  • each coil 3 is preferably arranged on the same spherical surface. Furthermore, four coils 7 are provided, which generate a magnetic gradient field Gx (i.e. a magnetic field, the strength of which changes linearly in one direction) which also runs in the z direction, but whose gradient runs in the x direction.
  • Gx i.e. a magnetic field, the strength of which changes linearly in one direction
  • a magnetic gradient field Gy running in the z-direction with a gradient in the y-direction is generated by four coils 5, which can have the same shape as the coils 7, but are arranged offset by 90 ° with respect to them. Only two of these four coils are shown in FIG.
  • a high-frequency modulated current is supplied to the high-frequency coil from a high-frequency generator during each high-frequency pulse.
  • the radio-frequency coil 11 or a separate radio-frequency reception coil is used to receive the nuclear magnetic resonance signals generated in the examination area.
  • the high-frequency coil 11 is connected on the one hand to a high-frequency generator 4 and on the other hand to a high-frequency receiver 6 via a switching device 12.
  • the high-frequency generator 4 contains a high-frequency oscillator 40 which can be digitally controlled by a control unit 15 and which supplies vibrations at a frequency corresponding to the Larmor frequency of the atomic nuclei to be excited at the field strength generated by the coils 1.
  • the output of the oscillator 40 is connected to an input of a mixer 43.
  • the mixer stage is supplied with a second input signal from a digital-to-analog converter 44, the output of which is connected to a digital memory 45. Controlled by the control device, a sequence of digital data words representing an envelope signal is read out of the memory.
  • the mixer 43 processes the input signals supplied to it so that the carrier oscillation modulated with the envelope signal appears at its output.
  • the output signal of the mixer 43 is fed via a switch 46 controlled by the control device 15 to a high-frequency power amplifier 47, the output of which is connected to the switching device 12. This is also controlled by the control device 15.
  • the receiver 6 contains a high-frequency amplifier 60, which is connected to the switching device and to which the nuclear magnetic resonance signals induced in the high-frequency coil 11 are supplied, the switching device having to have the corresponding switching state.
  • the amplifier 60 has a mute input controlled by the control device 15, via which it can be blocked, so that the gain is practically zero.
  • the output of the amplifier is connected to the first inputs of two multiplicative mixer stages 61 and 62, each of which corresponds to the product of its input signals Deliver output signal.
  • a signal with the frequency of the oscillator 40 is fed to the second inputs of the mixer stages 61 and 62, a phase shift of 90 ° between the signals at the two inputs. This phase shift is generated with the aid of a 90 ° phase shifter 48, the output of which is connected to the input of the mixer 62 and the input of which is connected to the input of the mixer 61 and to the output of the oscillator 40.
  • the output signals of the mixer 61 and 62 are each fed to an analog-to-digital converter 65 and 66 via low-pass filters 63 and 64, which suppress the frequency supplied by the oscillator 40 and all frequencies above and allow low-frequency components to pass through. This converts the analog signals of the circuit 61... 64 forming a quadrature demodulator into digital data words which are fed to a memory 14.
  • the analog-to-digital converters 65 and 66 and the memory 14 receive their clock pulses from a clock pulse generator 16, which can be blocked or released by the control device 15 via a control line, so that only in a measuring interval defined by the control device 15 is that of the High-frequency coil 11 supplied, transposed into the low-frequency range signals can be converted into a sequence of digital data words and stored in the memory 14.
  • the data words stored in the memory 14 are fed to a computer 17, which uses a discrete Fourier transformation to determine the spectrum of the nuclear magnetization and to use a suitable display unit, e.g. a monitor 18.
  • FIG. 3 shows the position of the components essential for the spectroscopic examination on a frequency scale which indicates frequency deviation normalized to the Larmor frequency of TMS (tetramethylsilane) compared to the Larmor frequency of TMS.
  • the Larmor frequency of TMS is therefore zero, while the Larmor frequency W of water is 4.7 ppm.
  • Lactic acid contains a line M2 at about 1.3 ppm, which comes from the CH 3 group of lactate. This CH 3 group is scalarly coupled to a CH group of the lactic acid molecule, whose Larmor frequency M1 is 4.1 ppm. In the immediate vicinity of component M2 there is a line L1 (at approx.
  • Fig. 3 the frequency spectrum of a binomial high-frequency pulse is also indicated schematically by a dashed line F.
  • Such high-frequency pulses are used as frequency-selective pulses in the method explained in more detail with reference to FIG. 4. It can be seen that the frequency components of these pulses have the value 0 for the water line W and their maximum for the line M2 of lactic acid.
  • the nuclear magnetization of water - and de facto not that of the lactic acid component M1 - is stimulated, but the lactic acid component M2, the coupled lipid components L1 and L2 and the other lipid components not shown in FIG. 3 in this frequency range.
  • FIG. 4 shows the temporal course of the signals in a sequence that is used for localized spectroscopy, among others. is also suitable in the area of the human heart.
  • the sequence is repeated enough times to achieve a sufficient signal / noise ratio.
  • the sequence begins with a frequency-selective 90 ° high-frequency pulse HF1, a binomial (1331) pulse (first line).
  • a binomial high-frequency pulse consists of a sequence of partial pulses, the associated flip angles of which are in the same relationship to one another as the binomial coefficients.
  • the temporal spacing of the partial pulses from one another and the frequency of the carrier oscillation effective within the partial pulses are dimensioned such that the frequency spectrum of the binomial high-frequency pulse disappears from water at the Larmor frequency W and has its maximum at least approximately at the Larmor frequency M2 of lactate.
  • the high-frequency pulse HF2 the center of which is 1/2 J from the center of the pulse HF1, where J is the scalar coupling constant of lactic acid (approx. 7 Hz), has the same time profile as HF1 - if one looks at the phase position of the Carrier vibration is absent. Between these two high-frequency pulses, the sequence comprises a hard (broadband) 180 ° high-frequency pulse HF3.
  • the carrier oscillation which is active during the high-frequency pulse HF3 must have the same or the opposite phase position as during the first or third sub-pulse of HF1. If HF2 has the same phase position as HF1, all components except M2 are suppressed so that lactate can be detected.
  • phase position of HF2 is offset by 90 ° compared to that of HF1, M2 and also the coupled lipid components L1, L2 are suppressed, so that a detection of the uncoupled lipid components L1, L2 is possible. This is described in detail in the publications mentioned at the beginning.
  • a further frequency selector is used after the RF pulse HF2 tive high-frequency pulse HF4, whose spectrum disappears at the water line W and has its maximum at M2 - corresponding to curve F in Fig. 3.
  • HF4 is preferably a 180 ° high-frequency pulse, for example in the form of a binomial (2B62) pulse.
  • a magnetic gradient field is switched on and off between the high-frequency pulses HF2 and HF4 and after HF4 - in this case the field Gz.
  • the size of the gradient and the time profile are chosen such that the time integral over Gz before HF4 is as large as after HF4.
  • the sequence following the radio frequency pulse HF4 comprises three 180 ° radio frequency pulses HF5, HF6 and HF7, each of which has a magnetic gradient field Gx, Gy and Gz (second , third and fourth lines of FIG. 4) are accompanied, the gradients of which are perpendicular to one another.
  • the detection is thus limited to a partial volume, the location and size of which is determined by the frequency of these pulses, their bandwidth and the strength of the gradient.
  • the gradient fields Gx, Gy and Gz are preferably effective with increased amplitude and such a time profile that the time integral over the magnetic gradient field up to the center of the assigned pulse is just as large as the time integral over the Gradient field after this time.
  • the time course of the gradient fields Gx..Gz has no influence on the nuclear magnetization within the selected partial volume, but on the nuclear magnetization in the examination area outside the partial volume, which is dephased as a result.
  • the high-frequency pulse HF4 and the gradient field Gz which is symmetrical over time, are generated in the middle of a time period T which begins at the center of the high-frequency pulse HF2.
  • the nuclear magnetic resonance signal developing in the selected partial volume is sampled according to the fifth line of FIG. 4 in a time interval, the center of which from the end of the time period T has the time interval (2N + 1 ) / 2J, where N is an integer, preferably 0 or 1.
  • the clock generator 16 is released so that the digitized nuclear magnetic resonance signal transposed into the low frequency range can be subjected to a discrete Fourier transformation in the computer 17, preferably after the nuclear magnetic resonance signals detected after repeated repetition of the described sequence in the sampling interval have been summed.
  • binomial high-frequency pulses were used as frequency-selective high-frequency pulses, but other frequency-selective pulses can also be used, for example the so-called DANTE pulses.
  • the angle by which the nuclear magnetization of components M2 or L1 etc. is tilted by the high-frequency pulse HF4 does not necessarily have to be 180 °; it can also be smaller, but then the amplitude of the nuclear magnetic resonance signals also decreases.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)
  • Measuring Magnetic Variables (AREA)
EP19910201832 1990-07-20 1991-07-12 Nuclear magnetic resonance spectroscopy procedure Withdrawn EP0467467A3 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE4023128 1990-07-20
DE4023128A DE4023128A1 (de) 1990-07-20 1990-07-20 Kernresonanz-spektroskopieverfahren

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EP0467467A2 true EP0467467A2 (fr) 1992-01-22
EP0467467A3 EP0467467A3 (en) 1992-10-21

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EP19910201832 Withdrawn EP0467467A3 (en) 1990-07-20 1991-07-12 Nuclear magnetic resonance spectroscopy procedure

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US (1) US5247255A (fr)
EP (1) EP0467467A3 (fr)
JP (1) JPH04307029A (fr)
DE (1) DE4023128A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0597785A1 (fr) * 1992-11-13 1994-05-18 Sadis Bruker Spectrospin, Societe Anonyme De Diffusion De L'instrumentation Scientifique Bruker Spectrospin Procédé d'excitation et d'acquisition de signaux de résonance magnétique nucléaire, notamment dans l'eau légère
CN103969610A (zh) * 2013-02-01 2014-08-06 西门子公司 采集磁共振数据和确定b1磁场的方法及磁共振设备

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0322006A2 (fr) * 1987-11-25 1989-06-28 Philips Patentverwaltung GmbH Procédé de spectroscopie par résonance magnétique nucléaire
EP0392574A2 (fr) * 1989-03-04 1990-10-17 Philips Patentverwaltung GmbH Procédé pour la spectroscopie à résonance nucléaire localisée et dispositif pour son exécution

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5111819A (en) * 1988-11-25 1992-05-12 General Electric Nmr imaging of metabolites using a multiple quantum excitation sequence

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0322006A2 (fr) * 1987-11-25 1989-06-28 Philips Patentverwaltung GmbH Procédé de spectroscopie par résonance magnétique nucléaire
EP0392574A2 (fr) * 1989-03-04 1990-10-17 Philips Patentverwaltung GmbH Procédé pour la spectroscopie à résonance nucléaire localisée et dispositif pour son exécution

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
MAGNETIC RESONANCE IN MEDICINE. vol. 6, no. 3, March 1988, DULUTH,MN US pages 334 - 343; G.C.MCKINNON ET AL.: 'Localized Double-Quantum Filter and Correlation Spectroscopy Experiments' *
MAGNETIC RESONANCE IN MEDICINE. vol. 8, no. 3, November 1988, DULUTH,MN US pages 355 - 361; G.C.MCKINNON ET AL.: 'A One-Shot Lactate-Editing Sequence for Localized Whole-Body Spectroscopy' *
MAGNETIC RESONANCE IN MEDICINE. vol. 9, no. 2, February 1989, DULUTH,MN US pages 254 - 260; A.KN]TTEL ET AL.: 'Single-Scan Volume-Selective Spectral Editing by Homonuclear Polarization Transfer' *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0597785A1 (fr) * 1992-11-13 1994-05-18 Sadis Bruker Spectrospin, Societe Anonyme De Diffusion De L'instrumentation Scientifique Bruker Spectrospin Procédé d'excitation et d'acquisition de signaux de résonance magnétique nucléaire, notamment dans l'eau légère
FR2698177A1 (fr) * 1992-11-13 1994-05-20 Sadis Bruker Spectrospin Procédé d'excitation et d'acquisition de signaux de résonance magnétique nucléaire, notamment dans l'eau légère.
US5475308A (en) * 1992-11-13 1995-12-12 Sadis Bruker Spectrospin Societe Anonyme De Diffusion De L'instrumentation Scientifique Bruker Spectrospin Process for the excitation and acquistion of nuclear magnetic resonance signals, particularly in light water
EP0913700A2 (fr) * 1992-11-13 1999-05-06 Bruker Sa Procédé d'excitation et d'acquisition de signaux de résonance magnétique nucléaire, notamment dans l'eau légère
EP0913700A3 (fr) * 1992-11-13 1999-07-21 Bruker Sa Procédé d'excitation et d'acquisition de signaux de résonance magnétique nucléaire, notamment dans l'eau légère
CN103969610A (zh) * 2013-02-01 2014-08-06 西门子公司 采集磁共振数据和确定b1磁场的方法及磁共振设备

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Publication number Publication date
DE4023128A1 (de) 1992-01-23
US5247255A (en) 1993-09-21
EP0467467A3 (en) 1992-10-21
JPH04307029A (ja) 1992-10-29

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